XML code:
<?xml version="1.0" encoding="UTF-8"?>
<SkinInfo>
<Information>
<Name>Half-Blood Prince</Name>
<Description>I have taken my Harry Potter obsession to a new level!
I'm not sad, I'm just dedicated. </Description>
<Version>1.0</Version>
<Compatibility>
<MsgVersion Major="8" Minor="5"/>
</Compatibility>
</Information>
<MessengerSkin>
<ResGroup>
<Restrictions>
<MsgVersions>
<Version Major="8" Minor="5"/>
</MsgVersions>
</Restrictions>
<Resources>
<New>
<Pictures>
<Picture Id="59000">
<File>images/59000.png</File>
</Picture>
</Pictures>
</New>
<Replace>
<Windows>
<Styles>
<Style Id="947">
<File>styles/msgres_4005_947.txt</File>
</Style>
</Styles>
</Windows>
</Replace>
</Resources>
</ResGroup>
</MessengerSkin>
</SkinInfo>
Copy the style 947 to a folder named "styles". Open the file, look for:
Element[id=atom(mainwndcontainer)]
{
Background:rcbkd(20061);
}
and change it to:
Element[id=atom(mainwndcontainer)]
{
Background:rcbkd(59000);
}
/ 
